Refrigeration & Air-Conditioning Practice Set-3

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1. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

2. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Sub-cooling or under-cooling

None of these

Normal cooling

3. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

4. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

5. Rating of a domestic refrigerator is of the order of

10 tons

5 tons

0.1 ton

40 tons

6. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Wet bulb temperature of air

Ambient air temperature

Dry bulb temperature of air

7. For obtaining high COP, the pressure range of compressor should be

High

Low

Any value

Optimum

8. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

15 bar

30 bar

9. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Centrifugal

Miniature sealed unit

10. The capillary tube, as an expansion device, is used in

All of these

Room air conditioners

Domestic refrigerators

Water coolers

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11. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

5

6

0.2

12. Freon group of refrigerants are

Nontoxic and non-inflammable

Inflammable

Non-inflammable and toxic

Toxic

13. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-77.7°C

-56.6°C

14. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More

Same

More for small capacity and less for high capacity

15. The curved lines on a psychrometric chart indicates

Dew point temperature

Wet bulb temperature

Dry bulb temperature

Relative humidity

16. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Involves no change in volume

Takes place at constant entropy

Takes place at constant pressure

17. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser

Absorber

Condenser, absorber and separator (rectifier)

18. The boiling point of ammonia is

-10.5°C

-33.3°C

-77.7°C

-30°C

19. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

20. A bootstrap air cooling system has

Four heat exchangers

Two heat exchangers

Three heat exchangers

One heat exchanger

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21. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(C) The warm air increases the rate of radiation of heat from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

22. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

9: 1

1: 3

1: 1

23. Which of the following cycles uses air as the refrigerant?

Carnot

Bell Coleman

Ericson

Stirling

24. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Rankine

Rankine

Reversed Carnot

25. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Always more than unity

Any one of the above

Equal to unity

26. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

3.33

4.33

1.33

27. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.67

0.4

0.376

28. Most thermostatic expansion valves are set for a superheat of

5°C

20°C

10°C

15°C

29. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Evaporator and compressor

Compressor and condenser

Receiver and evaporator

30. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Brine

Carbon dioxide

Ammonia

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31. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

32. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Wet vapour

Dry saturated vapour

Superheated vapour

33. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(C) Sum of (A) and (B)

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

34. Critical temperature is the temperature above which

Water will never evaporate

A gas will never liquefy

Water will evaporate

A gas will immediately liquefy

35. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Good electrical conductor

High risibility with oil

Low boiling point

36. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

None of these

Negative

Zero

37. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Unpredictable

Equally

More

38. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Much below critical temperature

Near critical temperature of refrigerant

39. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Detect liquid in vapour

40. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

1

5.12

Refrigeration & Air-Conditioning Practice Set-3

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